class Dog:

    """一次模拟小狗的简单尝试"""
    def __init__(self, name, age):
        """初始化name和age"""
        self.name = name
        self.age = age

    def sit(self):
        """模拟小狗收到命令时,坐下"""
        print(f"{self.name} is now sitting.")

    def roll_back(self):
        """模拟小狗收到命令打滚"""
        print(f"{self.name} rolled back.")


my_dog = Dog("Willie", 6)
your_dog = Dog('Lucy',3)

print(f"my dog's name is {my_dog.name}")
print(f"my dog is {my_dog.age} years old")
my_dog.sit()

print(f"\nyour dog's name is {your_dog.name}")
print(f"your dog is {your_dog.age} years old")
my_dog.sit()